Jupiter’s Moons: 10 More Found, 79 Known

Wednesday, July 18th 2018 12:20 PM

After the discovery of Jupiter's four Galilean satellites in 1610, astronomers struggled to find 10 more in the 3½ centuries that followed. Today the IAU's Minor Planet Center announced that a search team led by Scott Sheppard (Carnegie Institution for Science) has identified 10 new moons of Jupiter, bringing the known total to 79 — the most of any planet in our solar system. Of those, Sheppard has led the searches that discovered 51 of them. Dozens of Jupiter's moons circle the planet in a swarm of distant orbits and travel in a retrogradedirection, that is, opposite that of the planet's spin. Their orbits cluster in three groups of 15 to 20 objects, named for members Ananke (discovered in 1951), Carme (1938), and Pasiphae (1908). Most likely each of these moonlet "families" represent fragments of larger precursors that were shattered by collisions early in Jupiter's history. Of the 10 new finds, seven of them are among these retrograde objects. Two of them orbit...

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Astronomers in Australia are eager for a special celestial alignment this week that could tell them more about one of the most intriguing candidates for hosting life beyond Earth. That's because for a brief 4 minutes late Wednesday night (July 18) local time, Saturn's moon Titan will slip directly between Earth and a bright star. The rare alignment, formally called an occultation, will let astronomers study light streaming through the layers of Titan's hazy atmosphere. "It will be like an eclipse of the sun with the moon passing in front, but on a very subtle scale," David Coward, an astronomer at the University of Western Australia, told The West Australian, a local newspaper. "This eclipse forms a track across the Earth, and as Titan passes in front of the star, the light illuminates its atmosphere and allows scientists to use the data to work out the composition. The stars have to line up, literally." Scientists stuck on Earth have been observing o...

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2018 features two lunar eclipses, one in January and the other in July. On Jan. 31, there was a spectactular Super Blue Blood Moon eclipse. The July 27 Blood Moon will be the longest total lunar eclipse of the 21st century. Both will be total lunar eclipses, when the full moon passes through Earth's shadow. Lunar eclipses are visible from anywhere on Earth where it is nighttime. However, the duration of the eclipse  you see will depend on how close to moonrise or moonset the eclipse starts in your location. During total lunar eclipses, the moon turns a deep red color when it enters the depths of Earth's shadow. So why doesn't the moon just look like it's in darkness? The color change happens because Earth's atmosphere acts as both a lens and a scattering medium for the sun's light. As light passes through any medium, it slows down a bit, and bends. So some sunlight gets bent toward the moon's surface as it passes through Earth's atmosphere during an ec...

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Cosmic rays travel to Earth at relativistic speeds from deep space, but their origins have puzzled astronomers for over a century. Yesterday (July 12), an international team of scientists announced they had tracked an associated particle back to its origin, revealing for the first time one source of cosmic rays.  The discovery is a triumph of multimessenger astronomy, in which scientists use multiple types of signals — in this case, electromagnetic waves and ghostlike particles known as neutrinos — to probe cosmological questions impossible to answer the old-fashioned (one-message) way.  The multimessenger-astronomy era dawned in October 2017, when researchers announced that they'd observed gravitational waves and light emitted by a pair of merging neutron stars. And the trend continues with the new discovery. "Today, we're really excited to report [that] now we know something about cosmic accelerators in the joint detection of neutrinos and ga...

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This Week’s Sky at a Glance, July 13 – 21

Friday, July 13th 2018 09:32 AM

Friday, July 13 • Cassiopeia is now well past its annual bottoming out due north. Look for its W pattern climbing low in the north-northeast after dark. The farther north you live, the higher it will be. Saturday, July 14 • As twilight fades, see if you can catch the Moon over Mercury very low in the west, well to the lower right of Venus as shown here. Your best view may be about 45 minutes after sunset. • One hour after sunset, as twilight fades further and the stars are coming out, you'll find the two brightest stars of summer, Vega and Arcturus, about equally near the zenith: Vega toward the east, shining very pale bluish white, and Arcturus toward the southwest, pale yellow-orange. Sunday, July 15 • Moon and Venus: a lovely couple!Hanging dramatically in the west during twilight will be quite the eye-catcher: Venus and the crescent Moon closely paired. How closely depends on where you are. Seen at the time of dusk in North America's eastern...

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Blazars Explained

Thursday, July 12th 2018 10:53 AM

  On Thursday, researchers announced that they’d caught a single, tiny, high-energy particle called a neutrino that had rained down on Earth from a supermassive black hole some 4 billion light-years away. Astrophysicists are excited because this is only the third identified cosmic object they’ve managed to collect the elusive particles from — first the Sun, then a supernova that went off in a neighboring galaxy in 1987, and now a blazar. So, what is a blazar, anyway? A Cosmic Engine At the center of most galaxies — including our own Milky Way — there’s a gargantuan black hole that can have the mass of millions or even billions of Suns. In some galaxies, this supermassive black hole may collect a swirling disk of gas, dust and stellar debris around it to eat from. As material in the disk falls toward the black hole, its gravitational energy can be converted to light, making the centers of these galaxies ver...

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Lunar Landscapes Love Affair

Wednesday, July 11th 2018 09:11 AM

I was recently asked a question that caught me off guard: "Why, after doing it for more than half a century, do I still image the Moon?" The question caught me off guard primarily because I simply think, “This is what I do!  It is my niche in astronomy.” But the more I thought about the question, the more intrigued I became by it. After all, taking close-up photos of the Moon is not something many people do, and over the years I seem to have become good at it. The more I thought about it, the more I knew there had to be some underlying reasons for my loony... er... lunar activity.   It is true that NASA's spacecraft have imaged the Moon in orders of magnitude greater detail than I can achieve with my backyard telescope. From my earthly perspective, I can often achieve about a kilometer resolution on the Moon. NASA achieves under one-meter resolution with its Lunar Reconnaissance Orbiter. Science alone is obviously not the reason for my Moon p...

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Globular clusters might be younger than we thought

Tuesday, July 10th 2018 08:53 AM

The Milky Way globular cluster Omega Centauri contains stars that are currently estimated to be between 10 billion and 12 billion years old. ESO/INAF-VST/OmegaCAM; Acknowledgement: A. Grado, L. Limatola/INAF-Capodimonte Observatory   Globular clusters are spherical associations of old stars, thought to have formed during the earliest days of our universe, nearly 14 billion years ago. They contain some of the oldest stars in our galaxy, and the same appears true for other galaxies as well. But new research led by astronomers at the University of Warwick is now challenging this belief, showing that globular clusters may be a full 4 billion years younger than previously thought. Published May 24 in Monthly Notices of the Royal Astronomical Society, the paper states that globular clusters may be closer to 9 billion years in age than the previously measured value of 13 billion years. How did this age discrepancy arise? The age of globular clusters has...

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First Confirmed Image of Newborn Planet

Monday, July 9th 2018 12:50 PM

Our understanding of planet formation is often shrouded in theoretical models. But now, scientists have directly observed a new planet in the gaseous disk around a young star about 370 light-years from Earth. The SPHERE instrument on the Very Large Telescope in Chile imaged the newborn planet PDS 70b.ESO / A. Müller et al. The search for new planets often starts with a survey of the heavenly regions where stars are born. Scientists at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany were doing just that when they focused their attention on the young star PDS 70. At 5 million to 6 million years old it is still accreting mass from its surrounding disk of gas and dust. The star —which is about the size of our Sun — was first discovered in 1992, but scientists using the Very Large Telescope’s SPHERE instrument hoped to see new details in its disk. To their surprise, they found a gap — a dark path — in the middle of the...

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Wheel-spoke Magnetic Field in Supernova 1987A

Saturday, July 7th 2018 11:05 AM

Supernova 1987A was the first stellar explosion witnessed with unaided eyes in more than 400 years. Its brightness, with a peak apparent magnitude of +2.9, was due in part to its proximity, as it's located in the Milky Way's largest satellite galaxy, the Large Magellanic Cloud. In the decades since its discovery, SN1987A has provided astronomers with a practically backyard laboratory to investigate how supernovae accelerate particles to speeds undreamed of by Earthbound physicists. Taken in 2006, this Hubble image shows the region around SN 1987A. The most prominent feature is the light-year-wide ring, where the supernova's shock wave slammed into clumps of material, causing them to glow as hotspots. The two bright objects are a pair of stars in the Large Magellanic Cloud.  Now, Giovanna Zanardo (University of Western Australia) and colleagues report the first-ever map of the magnetic field that courses through the hot gas surrounding the collapse star. The results appear in t...

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